It looks more like a vascular plant than an algae or moss, at least to me.
It seems like there are small, thread-like, opposite leaves. Is this correct? If so, can you see small green fruits in the leaf axils (joint between leaf and stem)? If there are, it is likely a naiad (Najas sp.) or a water starwort (Callitriche sp.). Naiads have pointed fruits, starworts have round ones. It could also be a bladderwort (Utricularia) as Msjinkzd suggests, a small Potamogeton, or...
Any chance you could get a friend with a macro-capable camera to photograph it?